Refactor macOS to use new objc2 features (#2465)

* Remove UnownedWindow::inner_rect

* Refactor custom view to use much less `unsafe`

The compiler fence is safe to get rid of now since `interpretKeyEvents` takes `&mut self`

* Refactor Window to use much less unsafe

* Refactor NSApplication usage to have much less unsafe

* Remove cocoa dependency

* Enable `deny(unsafe_op_in_unsafe_fn)` on macOS

Also re-enable clippy `let_unit_value` lint

* Remove #[macro_use] on macOS

* Refactor window delegate to use much less unsafe

src/platform_impl/macos/appkit/screen.rs

@@ -0,0 +1,64 @@
+use objc2::foundation::{CGFloat, NSArray, NSDictionary, NSNumber, NSObject, NSRect, NSString};
+use objc2::rc::{Id, Shared};
+use objc2::runtime::Object;
+use objc2::{extern_class, extern_methods, msg_send_id, ns_string, ClassType};
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSScreen;
+
+    unsafe impl ClassType for NSScreen {
+        type Super = NSObject;
+    }
+);
+
+// TODO: Main thread marker!
+
+extern_methods!(
+    unsafe impl NSScreen {
+        /// The application object must have been created.
+        pub fn main() -> Option<Id<Self, Shared>> {
+            unsafe { msg_send_id![Self::class(), mainScreen] }
+        }
+
+        /// The application object must have been created.
+        pub fn screens() -> Id<NSArray<Self, Shared>, Shared> {
+            unsafe { msg_send_id![Self::class(), screens] }
+        }
+
+        #[sel(frame)]
+        pub fn frame(&self) -> NSRect;
+
+        #[sel(visibleFrame)]
+        pub fn visibleFrame(&self) -> NSRect;
+
+        pub fn deviceDescription(
+            &self,
+        ) -> Id<NSDictionary<NSDeviceDescriptionKey, Object>, Shared> {
+            unsafe { msg_send_id![self, deviceDescription] }
+        }
+
+        pub fn display_id(&self) -> u32 {
+            let device_description = self.deviceDescription();
+
+            // Retrieve the CGDirectDisplayID associated with this screen
+            //
+            // SAFETY: The value from @"NSScreenNumber" in deviceDescription is guaranteed
+            // to be an NSNumber. See documentation for `deviceDescription` for details:
+            // <https://developer.apple.com/documentation/appkit/nsscreen/1388360-devicedescription?language=objc>
+            let obj = device_description
+                .get(ns_string!("NSScreenNumber"))
+                .expect("failed getting screen display id from device description");
+            let obj: *const Object = obj;
+            let obj: *const NSNumber = obj.cast();
+            let obj: &NSNumber = unsafe { &*obj };
+
+            obj.as_u32()
+        }
+
+        #[sel(backingScaleFactor)]
+        pub fn backingScaleFactor(&self) -> CGFloat;
+    }
+);
+
+pub type NSDeviceDescriptionKey = NSString;